An RFID tag is a radio-frequency transponder that receive RF power at a given frequency and converts that received RF power to DC power to power itself and to transmit an RF signal. U.S. Pat. No. 6,046,676 discloses a RFID tag that is used for identifying and for communicating with a computer. The RFID tag is self-powered from a so-called RF interrogation signal when the electronic device is not operational. The RFID tag is powered from the computer when it is communicating with the computer. The RFID tag is attached to the computer as part of the computer memory. This arrangement limits the size of the memory to that provided within the RFID tag.
A previously known two-port RFID device is the AT88RF001 by Atmel Corporation, San Jose, Calif. that is a stand-alone 13.56 MHz two-port RFID front-end device that has one RF antenna port and one serial memory port for connection to an external serial memory chip. This RFID device does not have provisions for interfacing with an external computer system. This RFID device provides power to the external serial memory chip. A problem with integrating this type of RFID device into an electronic system is that the external serial memory resides on a system bus with other devices. When an attempt is made to power the external serial memory via RF energy received via the RF antenna port, other devices on the system bus draw current from the RFID device because of I/O circuit leakages, shared power connections with memory devices, etc. These various current drains or leakage paths are not easily quantified or controlled.
What is desired is an RFID device that is isolated from the rest of an electronic system, to thereby eliminate leakage paths to other elements of the system. As a result, the amount of power to be supplied by the RFID device is only power that is consumed by the RFID device itself and the power required by the external memory.